Just some examples on how much is needed to take down Lugia. Seeing that Zekrom boasts the highest Attack (Base 150) stat while still getting a SE STAB move on Lugia is quite amazing. And seeing that Kyurem-W has litterally the strongest Blizzard ever, and BARELY KO's Lugia, you can see why Lugia + Multiscale has become one of the scariest things to face in Ubers. Sure, it's possible to OHKO it, but don't think it will be easy.

Well...
I don't think that it is possible to knock out Lugia in one hit with it's amazing stats.
But if you count Destiny Bond as a move then yes it can. Although it is unlikely that a Lugia will OHKO any Pokemon.
So Destiny Bond seems to be the only option for OHKO'ing a Lugia.
Sorry if this wasn't what you were looking for.